The invention relates to a process for reading a chain of code characters which is arranged on a transparent bottle or the like in the lower region of the same in an annular manner, by directing a camera through the neck of the bottle onto the lower region of the bottle, illuminating of the lower area of the bottle from outside and storing and decoding of the code character chain photographed with the camera.
U.S. Pat. No. 4,990,792 of the Applicant describes a process for introducing optically readable code characters onto the surface of containers, preferably plastic bottles, by producing cavities in the surface by means of a laser, so that the base of each code character is designed as a diffusely dispersing reflector. In the case of plastic bottles, this involves preferably multitrip PET bottles, i.e. PET bottles which are returned by the customer and then re-filled, which is intended to be done about 25 times per bottle. The code which according to this older German patent of the Applicant, is introduced by means of a laser, replaces, for example, the known Saint Gobain code of convex or depressed points, by means of which the blow die number is normally stated on the surface of the bottle, requires less time to apply than the known code and can record considerably more information. Moreover, it can be read more reliably. This reading takes place automatically with a reading head, for example, according to the further U.S. Pat. No. 4,852,415 of the Applicant. The reading head contains an optical electrical sensor which, by means of light guides, casts a beam of light sent out by a light source onto the surface of the bottle, and transmits a beam of light reflected by a code character back to a photoelectric receiver. For the reading procedure the bottle feed is interrupted when the bottle is opposite the sensor, and the bottle is rotated several times about its longitudinal axis, so that the sensor can record the chain of code characters several times.
This suspension of the feed and repeated rotation of each bottle opposite the sensor requires time, which should be as short as possible, as in inspection machines for re-fillable PET bottles the inspection capacity reaches 600 PET bottles/minute. Moreover, as multitrip plastic bottles become scratched more easily and are less stable in shape and resistant to ageing than glass ones, it can happen that with each refilling of the multitrip PET bottle, the process for the correct reading of its code creates further difficulties, because for example, the code character chain has altered its position or is noticeably blurred or indistinct. Furthermore, the known code-reading process is often made more difficult by the fact that bottles which are to be re-filled carry remains of labels or complete labels from the washing plant, or have been so badly scratched on the outside in use and for this reason create so much scattered light, that it is impossible to read the code correctly.
One code-reading process known from U.S. Pat. No. 4,250,405 avoids the last-mentioned problems by using for code-reading a camera which is so arranged that it points downwards through the neck of each bottle and is focussed on its base. A grid on the base of the bottle contains a code which indicates the number of the mould cavity in which the bottle has been manufactured. A code of nine characters is used, two of which indicate the beginning or end of the code. Light is projected from below through a gap onto the base of the bottle by means of an illumination source. In order to read the bottle code, its feed is interrupted underneath the camera, and the bottle is then rotated about its longitudinal axis. The code characters are provided in two concentric grid circuits on the base of the bottle. Each code character is composed of two bits, namely one in the outer grid circuit and one in the inner grid circuit. In order to read the code reliably, the bottle is rotated four times about its longitudinal axis during each reading procedure. The camera is a line-scanning camera which serially photographs the code characters passing the gap in the form of the graticule markings. This known reading process is certainly impaired less by external influences, as the camera photographs the code characters from the inside of the bottle, but it requires time and equipment on account of interruption of feed and repeated rotation of the bottles during each reading procedure, and on account of the apparatus necessary for clamping and rotating the bottle. The code used is costly, because the code character chain is composed of two concentric circular rings, which can only be provided on the bases of bottles. This would hardly permit more than mould cavity number information to be coded and would be applicable to glass bottles in any case. In this known process, working with code characters in two grid circuits cannot be avoided, however, because on the one hand each code character is composed of two bits, and on the other hand the beginning and end of a code character chain has not otherwise been able to be marked.
It is also already known from U.S. Pat. No. 4,644,151 to provide a code character chain in two rastered circles on the bottle wall above the bottom, the illumination and reading of these being performed, however, from the outside as in the Applicant's above mentioned U.S. Pat. No. 4,852,415. The difference is simply that in place of the light sensor there is a camera.
A code reading process is in fact already known from U.S. Pat. No. 3,963,918, in which the code character chain is composed of only one circular ring which is provided on the base of a glass or plastic bottle, but in any case in this known process all the above-mentioned problems would appear to occur. In this known process, the light of a lamp is directed from above through the neck of the bottle onto the bottle base, and the bottle does not have to be rotated about its longitudinal axis during the reading procedure. A light detector is provided underneath the bottle base and has a reading head which is rotated about the longitudinal axis of the bottle, for the serial recording of the code characters. This is to say, the so-called scanner technique is used for working, in which a reading head rotates instead of the bottle. The time expended does not become less, although possibly the expenditure on apparatus does, as it is easier to set a reading head rotating constantly in the same position and alignment than bottles, which have to be clamped and rotated in succession over the one and the same reading head in as identical as possible an alignment and position. In the case of this known process also, each code character is composed of several bits. In order that the beginning of the code character chain can be determined, a special character combination of four grid markings arranged close beside each other is provided with which reading-off is intended to begin. Data sampling preferably takes place several times, in order to increase the reading accuracy. Nevertheless, the use of a self-correcting code with parity markings is provided for this known process.
U.S. Pat. No. 3,991,883 describes a process and a device for the identification of a bottle, in which the code used corresponds to that used in the process described heretofore. A laser beam which is directed through the neck of the bottle onto the base of the bottle is used in order to illuminate the code character chain. Underneath the bottom of the bottle is arranged a mirror, which directs the emerging laser beam onto a sensor. For the reading procedure, it is necessary to set in rotation either the laser beam or, once again, the bottle, which is fraught with the problems described above.
Finally, from U.S. Pat. No. 3,745,314 are known a device and a process for identifying the mould cavity of a bottle, in which a lamp arranged over the bottle mouth and directed onto the bottom of the bottle and a reading unit arranged underneath the bottom of the bottle are at rest, but a rotatable prism is provided between the reading unit and the bottom of the bottle which directs the image of the bottom of the bottle via a condensing lens onto the reading unit and sets it rotating on the latter. The code character chain which is provided on the bottom of the bottle here again consists of two concentric rings. Because of the necessary relative movement between lamp and bottle on the one hand and reading unit on the other hand, which is created here by the rotating prism, the same problems arise as with the other known processes and devices in which this relative rotary movement is likewise necessary. With regard to the time expended at least, it is insignificant that a prism is rotated instead of the bottle or the reading device in order to achieve a serial reading of the code characters.
The problem of the invention is to improve a code-reading process of the type hereinbefore mentioned in such a way that the code can be read expending considerably less time and with a greater information content without any loss of accuracy.